1. Field of the Invention
The present invention relates to a chip resistor comprising an insulating substrate in the form of a chip, at least one resistor film formed on the substrate, a pair of terminal electrodes formed on the substrate to flank the resistor film, and a cover coat covering the resistor film.
2. Description of the Related Art
Conventionally, in a chip resistor of the above-described type, the cover coat covering the resistor film projects largely from a central portion of the upper surface of the insulating substrate, thereby providing stepped portions in the chip resistor. Therefore, when such a chip resistor is mounted on a printed circuit board with the resistor film facing the printed circuit board, the chip resistor is often disadvantageously inclined with one end thereof rising to be away from the circuit board.
JP-A-8-236302 discloses a chip resistor capable of solving such a problem. Specifically, as shown in FIG. 9 of JP-A-8-236302, the disclosed chip resistor is provided with auxiliary upper electrodes formed on the upper electrodes provided at opposite ends of the resistor film to partially overlap the cover coat. With such an arrangement, no stepped portions or only small stepped portions are provided in the chip resistor, whereby the chip resistor is prevented from inclining when mounted on a printed circuit board with the resistor film facing the printed circuit board.
However, in such a prior art chip resistor, the auxiliary upper electrodes do not project largely relative to the obverse surface of the cover coat. Therefore, when the chip resistor is mounted on a printed circuit board with the resistor film facing the printed circuit board, the cover coat is brought into contact with or comes too close to the printed circuit board. Since the printed wiring board in such a state is likely to be influenced by the heat generated at the heat resistor, the rated value of the chip resistor cannot be enhanced. Further, since the auxiliary upper electrodes do not project largely relative to the obverse surface of the cover coat, the insulating substrate is also located close to the printed wiring board. Therefore, the difference in thermal expansion between the insulating substrate and the printed circuit board cannot be absorbed, which results in removal of electrodes from the insulating film.
The above problems may be solved when a portion of the auxiliary upper electrode, which overlaps the cover coat, is bulged so that the upper surface of that portion becomes higher than the obverse surface of the cover coat. In such a case, however, when the chip resistor is mounted on a printed circuit board, a gap is defined between the printed circuit board and opposite ends of the chip resistor. In soldering, therefore, there is an increased possibility that the chip resistor is inclined with one of the opposite ends rising from the printed circuit board.
However, to make the entirety of the auxiliary upper electrode thick for making the upper surface thereof higher than the obverse surface of the cover coat, a larger amount of material need be used for making the auxiliary upper electrode, which leads to an increase of the manufacturing cost.